Author Topic: Plastic uniflow clunk tanks (Read 2333 times)

John Miller · « **on:** August 06, 2007, 10:03:18 AM »

Bob Z's adaptation of the hopper tank is pretty cool, but, since a lot of folks seem to be having troubles using plastic RC clunk tanks for stunt, whether 2 or 4 stroke, I thought I'd show a drawing of my uniflow setup for those tanks.

They work very well in my planes, and are easy to adjust tank hieght without having to physically move the tank.

John Miller

Wayne J. Buran · « **Reply #1 on:** August 07, 2007, 05:05:50 AM »

Bill, can you orient this in a fuselage with an inverted setup. I am confused and I would like to try this setup. Thanks
Wayne

PatRobinson · « **Reply #2 on:** August 07, 2007, 08:19:15 AM »

John,
I feel like I walked into the middle of a conversation so my question is:
What exactly did Bob Z. do with his hopper tank. I did a search here and on SSW and found a reference to Eagle-Hopper tank in an Argus. Googled Eagle-Hopper and found references to paint guns and antiques.
I have built several chicken-hopper tanks of different configurations and shapes so I was curious about the topic but need clarification to understand your reference. Thanks.
Pat Robinson

John Miller · « **Reply #3 on:** August 07, 2007, 08:59:54 AM »

Sorry Pat, I was refering to a post that at the time was very near to this one. Basically Bob moved the "Chicken Hopper" to the rear of the tank. Allows the benifits of the Hopper in a narrow stunt fuselage. He has posted some 3D computer images that show what he's done.

Wayne, in answer to your question, I'm using this style of tank in my Legacy, Vector, and All American Eagle classic ship. All are inverted engines. Perhaps what is confusing is the way I drew the illustration, and the orthographic projection. Since the main view, is of the top of the tank, the standard orthographic projection shows the front of the tank on it's side. The only reason for showing the front was to show the way the tubes were placed. I have attached another image with the orthographic projection based on the front view to clear this up.

Kim Mortimore · « **Reply #4 on:** August 07, 2007, 11:52:30 AM »

John,
Based on your experience, would you say that clunk tanks are less sensitive to tank height than metal tanks?

Thanks,
Kim Mortimore

John Miller · « **Reply #5 on:** August 07, 2007, 01:02:47 PM »

Well, a good question.

I would say at first thought no, they seem to be about the same, but tanks set up like this, are easier to fine tune, very quickly, without having to remove, or re-shim the tank. That, with the weight savings, and ease of finding the tanks, have made them my tank of choice on most of my planes.

Wayne J. Buran · « **Reply #6 on:** August 07, 2007, 02:31:43 PM »

So, If I am looking at the drawing correctly, the fuel pick up is towards the inside instead of the outside, right. I am looking at the tank in launch position. Correct? Do you plumb the uniflow tube to the outside of the fuselage or is it inside?
Thanks
Wayne

John Miller · « **Reply #7 on:** August 07, 2007, 05:17:46 PM »

Hi Wayne,

OK, let's see if I can shed some more light on this for you.

Yes, in the last image, you are looking at the front of the tank. The uniflow uses the outboard bottom hole because the line must not interfere with the pickup clunk line. The uniflow is bent to make it come very close to the outside edge of the tank, at about mid way down the tank interior. The uniflow line is also bent on the outside to allow you to more easily rotate the uniflow to adjust the virtual tank height. It also will give you a referrence to how far you've rotated the uniflow.

The pickup tube occupies the inside bottom hole, and is slightly bent to angle the pickup to the outside rear of the tank. Rotating this line will not make a diferrence on the apparent tank height.

The overflow line, makes a bend to the upper inside edge of the tank. The illustration shows the best of all worlds regarding the position of the over flow inside the tank, but in practise, it can be further back , but, must be to the upper inside edge to work best. Always cap the overflow whether you're running pressure or not.

The top view, shows the tank as if you were standing at the front of the model, looking down on it.

Hope this helps.

Best wishes,

John Miller

Wayne J. Buran · « **Reply #8 on:** August 07, 2007, 05:50:58 PM »

Thanks John, much clearer now. I will give it a try.
Thanks
Wayne

Jim Oliver · « **Reply #9 on:** August 07, 2007, 06:51:41 PM »

John,

Would you please show a sketch of how you terminate the uniflow line; is it turned into the slipstream or does it terminate inside the cowl, or

Thanks,

Jim

Wayne J. Buran · « **Reply #10 on:** August 08, 2007, 04:55:54 AM »

Maybe someone can chime in on whether the exit tube for the uniflow is effected by being into the wind, prop wash, or what ever. Does it matter which way its pointed or the inside diameter of the may be should be reduced at the exit. I have never figured that out.
Thanks
Wayne

John Miller · « **Reply #11 on:** August 10, 2007, 08:10:07 PM »

Sorry to have taken so long to answer these last two questions. I've been gone on a backpacking/fishing, trip up into the High Uintas of Utah.

First, since I always use muffler pressure, it's been a non-question for me. The reason I use muffler pressure is to make sure that I don't have a problem ging rich into the wind.

Non-pressure systems, though used by a lot of people, can have problems with going rich into the wind. Reducing the opening area of the Uniflow can help, but for me it's simply cured by using pressure.

So, for pressure, the uniflow line goes to the pressure tap on the muffler.

Non-pressure setups normally have the vent pointed into the airstream for some ram air pressure.

Last point, all of my setups using this tank set up have been presure from the muffler, to the uniflow. Zero problems.

L0U CRANE · « **Reply #12 on:** August 12, 2007, 09:08:57 PM »

Hey,John, HI!

The question about the orientation of the 'open' end of the uniflo vent is dealt with by a small detail some may have missed: John's uniflo vent tube touches the mid-length of the tank...

Hard-shell or whatever way it is built, if the pressure line ends too near the fuel pickup for the NVA, you may get bubbles. The separation John uses takes care of that. For a hard-shell (metal) tank, I've found using the overflow tube for muffler pressure to be more certain. That uncovers into air-space early in the run, so the pressure changes little.

As far as un-pressurized uniflo plumbing, I see the problem this way: the model carries a bit of excess velocity (relative the the air it flies through) coming past the downwind point, until drag, etc., scrub that off. (Tailwind boosts airspeed before that point.) Soo, the model comes into the zone where we want to start maneuvers with some excess airspeed - read Ram Pressure - on the open vent end. That makes for a bit richer engine condition. NOT reassuring...

Sleeving the open end down reduces the force (which is the result of Pressure X Area) on the fuel in the tank shell. So, richening is reduced a bit.

This works for some engines. I've not had nice results with a Fox 35 on muffler pressure, but the reduced inlet uniflo open end has done nicely. Haven't yet tried a soft tank with a Fox 35...

Peter Germann · « **Reply #13 on:** August 13, 2007, 02:22:01 AM »

After repeatedly catching very small bugs with the forward facing uniflow vent (found them in the fuel filter twice) I have connected the vent, by means of a 2 in. long fuel tube, to the space behind the engine; i.e inside the cowl. No further problem, not even a noticable change of the needle setting. Jett .61 and Ro-Jett .76, both on pipe (no pressure)

Dick Fowler · « **Reply #14 on:** August 13, 2007, 06:55:52 AM »

Lou..."Sleeving the open end down reduces the force (which is the result of Pressure X Area) on the fuel in the tank shell. So, richening is reduced a bit."

Usually we are on the same page but I'm not sure I see the above the same way you do. While its true that the force is pressure X area, I think it isn't the causative factor. In our case the air is entering the tank and if you have 7 in. H2O above atmosphere at the vent, no matter the size of the hole of the uniflow vent, the internal pressure of the tank will eventually reach that 7 in. H20 above atmospheric pressure. The key word here is eventually. By restricting the opening and adding resistance to flow in the uniflow vent, the way I see it is that the rate at which the internal tank pressure changes is reduced so that these transient tank pressure changes as the plane flies around the circle are damped.

t michael jennings · « **Reply #15 on:** May 17, 2010, 08:18:16 AM »

Gentlemen,

Mr. Miller's Plastic Fuel Tank's Uniflow Setup looks like a good idea. This appears to be a better method of adjusting the fuel head when the model is sitting still.

In flight, the fuel head should be the distance from the plastic tank's outboard wall to the fuel level toward the inboard wing. This would be perpendicular to the measurement while the model is setting still.

How many pilots are using Mr. Millers piping of the Uniflow vent inside their Plastic Fuel Tank verses solderning the uniflow vent to the fuel pickup?

Thanks for your responses.

t michael jennings

Knoxville, TN

Author Topic: Plastic uniflow clunk tanks (Read 2333 times)

John Miller

Plastic uniflow clunk tanks

Wayne J. Buran

Re: Plastic uniflow clunk tanks

PatRobinson

Re: Plastic uniflow clunk tanks

John Miller

Re: Plastic uniflow clunk tanks

Kim Mortimore

Re: Plastic uniflow clunk tanks

John Miller

Re: Plastic uniflow clunk tanks

Wayne J. Buran

Re: Plastic uniflow clunk tanks

John Miller

Re: Plastic uniflow clunk tanks

Wayne J. Buran

Re: Plastic uniflow clunk tanks

Jim Oliver

Re: Plastic uniflow clunk tanks

Wayne J. Buran

Re: Plastic uniflow clunk tanks

John Miller

Re: Plastic uniflow clunk tanks

L0U CRANE

Re: Plastic uniflow clunk tanks

Peter Germann

Re: Uniflow vent

Dick Fowler

Re: Plastic uniflow clunk tanks

t michael jennings

Re: Plastic uniflow clunk tanks